phys: clarify intensity variables
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@ -698,7 +698,7 @@ $$E\propto I\propto A^2$$
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**Malus's law** states that for a polarised wave of energy $E_0$, the amplitude from the second filter, where $\theta$ is the angle between the polariser and the analyser, such that:
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$$E=E_0\cos\theta$$
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And so:
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And so, where $I$ is the intensity of the polarised/analysed light, $I_0$ is the intensity of the plane-polarised light, and $\theta$ is the angle between the polariser and the analyser:
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$$I=I_0\cos^2\theta$$
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When **unpolarised light** passes through a polariser, the average result of $I\cos^2\theta$ is $\frac{1}{2}$, so the intensity of polarised light is **half** of the intensity of unpolarised light.
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